1. Field of the Invention
The present invention relates to image forming apparatuses of the electrophotographic method and particular by to a separation section for separating transfer sheet from an image carrier.
2. Description of Related Art
In an electrophotographic process, as is well known, a toner image is formed on a transfer sheet by forming, developing and transferring an electrostatic latent image, and the electrophotographic process involves a separation operation for separating the transfer sheet from an image carrier. The most widely adopted separation technique removes electric charge from transfer sheet so that the electrostatic attractive force between an image carrier and transfer sheet is weakened or eliminated, thereby separating transfer sheet.
In this case, the separation is made taking advantage of the rectilinear property of transfer sheet due to its rigidity and the drum shape of an image carrier or the arc shape of a belt-like image carrier formed by roller support.
However, since a transfer sheet comes in different types, including thin sheet with low rigidity, or due to changes in environmental or other conditions, electrostatic separation taking advantage of the rigidity of transfer sheet cannot always ensure separation by itself and there may arise a case where separation is not achieved, which has led to the use of a separation pawl for physically separating transfer sheet.
In addition, the separation part of the separation pawl abuts an image carrier during the transfer operation, in which a toner image is transferred on transfer sheet. Therefore, if the separation pawl abuts only one part of an image carrier, wear occurs intensively only at this part, thereby reducing the service life of the image carrier. In order to avoid this, the separation pawl is usually moved in the axial (width) direction of an image carrier.
As apparatuses using the separation pawl, image forming apparatuses have been disclosed wherein the housing of a drum cartridge (process cartridge), a separation pawl support which is attached to the housing and the attaching structure thereof are all made of resin (see, for example, Japanese Unexamined Patent Application Publication No. 09-269701, hereinafter referred to as Patent Document 1).
Patent Document 1 discloses an apparatus wherein the whole separation pawl support of the drum cartridge and the whole attaching structure thereof are made of resin similarly to the housing, thereby making it easy to manufacture the drum cartridge.
However, when a plurality of components constituting a separation section are made solely of resin, or materials of the same sort, the vibrations of a process cartridge are easily transmitted between components and the vibrations can easily trigger resonances among components. Furthermore, since the separation section is supported by the components of a process cartridge which are made of resin, it is even more susceptible to the effect of vibrations. As a result, the separation pawl vibrates and exerts force toward the image carrier at the separation part of the separation pawl in contact with the image carrier, which has resulted in scratches on the surface of the image carrier. The scratches deteriorated the quality of formed images.
FIG. 6 is a schematic view showing an example of the vibration state of the tip of the separation pawl 44. In FIG. 6, position A in solid line is the reference position of the separation pawl 44 and positions B and C in dashed line are examples of the shifted tip.
In addition, an apparatus is also known wherein the housing of a process cartridge, a separation pawl support attached to the housing and the attaching structure thereof are all made of metal. Unfortunately, when they are made of metal as described above, since the support which supports the separation section and the engaging member of the separation section which is connected thereto are metal, there is no elasticity that resin components would have, and therefore vibrations are poorly absorbed and easily transmitted. Consequently, the surface of the image carrier has been scratched. Furthermore, as mentioned above, the slide member provided between the support and the engaging member for moving the separation pawl in the axial direction of the image carrier, among other things, has complicated the structure.